1. Field of the Invention
This invention relates to a start control system for an internal combustion engine of a type which starts the engine by utilizing oil pressure.
2. Description of the Related Art
Conventionally, in a start system for an internal combustion engine for an automotive vehicle, when the driver operates an ignition key to start the engine, electric power is supplied from a battery to an electric motor of a starter, whereby the electric motor forcibly causes rotation of a crankshaft of the engine, and at the same time an air-fuel mixture is supplied to cylinders of the engine. The air-fuel mixture thus supplied to cylinders is ignited to start the engine. Then, after the start of the engine, the driver releases the ignition key, whereby the electric motor is stopped.
Further, in recent years, a start control system for an internal combustion engine for an automotive vehicle has been employed which is capable of automatically stopping idling of the engine, e.g., when the driver is waiting for traffic lights to change or for a crossing gate to open, and then automatically restarting the engine when the vehicle is started. In the start control system, the restart of the engine after the automatic stoppage of idling is carried out by causing the above start system to operate in response to a vehicle start operation by the driver. The driver""s vehicle start operation includes operating a clutch or a shift gear, releasing a brake, or stepping on an accelerator pedal. When the vehicle start operation is carried out, electric power is supplied from the battery to the electric motor of the starter, whereby the electric motor forcibly causes rotation of the crankshaft, and the mixture is supplied to the cylinders. The air-fuel mixture thus supplied to the cylinders is ignited to start the engine. According to this start control system, because idling is automatically stopped, as described above, e.g., when the driver is waiting for traffic lights to change, excellent fuel economy can be ensured.
However, the above start control system uses the battery as a power source for the electric motor of the starter, and the starting torque of the motor is small. Hence, the motor is generally combined with a reduction gear system. For this reason, during the start or restart of the engine, the crankshaft can only be rotated at a rotational speed which is considerably loser than an idling rotational speed, so that it takes much time for the engine to start actually. Further, during cranking of the engine there occurs torque variation due to compression and expansion of air within the cylinder of the engine, which causes variation in the rotational speed of the crankshaft. In this case, the rotational speed of the crankshaft driven by the electric motor is reduced due to increased viscous friction of lubricating oil in the engine and stabilized at a low level, so that the variation in the rotational speed of the crankshaft becomes large, which causes the reduction gear mechanism to produce untoward noises. As described above, because it takes much time before the engine is actually started to start the vehicle in response to the vehicle start operation by the driver, and vibrations of the engine and noises from the driving system, which are undesired by the driver, are caused during the start of the engine, the start control system degrades marketability of the vehicle.
To solve the problems, there was proposed a start control system for an internal combustion engine e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 60-85249, in which compressed air is utilized to start the engine. The start control system includes a compressor driven by rotation of a crankshaft and a reserve tank for storing compressed air supplied from the compressor. According to the system, in response to an engine start operation by an ignition key, the crankshaft is driven for rotation by using the compressed air in the reserve tank as a driving force source, whereby the engine is started. Also, for the restart of the engine, similar control is carried out in response to the engine start operation by the ignition key. Thus, the use of the compressed air makes it possible to obtain larger torque than the torque from the electric motor of the starter, thereby shortening the time period required for starting the engine. Further, it is possible to increase the engine rotational speed to the idling rotational speed in a short time period, thereby reducing vibration of the engine and noises caused during the start of the engine.
Further, there has been proposed another type of the start control system for an internal combustion engine, which includes a large-sized electric motor and a large-capacity battery, and is applied to a vehicle configured to travel by driving force from the large-sized electric motor and the internal combustion engine installed thereon, i.e., a so-called hybrid vehicle. Some of the start control systems of this type are capable of not only starting the engine by the large-sized electric motor, but also automatically restarting the engine without the engine start operation by the ignition key. Through the use of the large-sized electric motor which generates considerably larger torque in comparison with the electric motor of the starter, this type of the start control system is capable of starting the engine in a shorter time period as well as reducing the vibrations of the engine. Further, because the engine can be automatically restarted without the engine start operation by the ignition key, high marketability of the system is ensured.
However, according to the above conventional start control system using compressed air, because the torque of the engine is employed as a driving force source for the compressor, it is impossible to drive the compressor during stoppage of the engine. For this reason, when compressed air within the reserve tank was consumed by an erroneous operation or the like before the stoppage of the engine, and no pressure has been stored within the tank, the engine cannot be started. Further, there is a limit to available high pressure of air, and it is required to provide a large-sized reserve tank so as to secure sufficient amount of compressed air for starting the engine, which results in an increase in the weight of the system and makes it difficult to provide space for accommodating the system. Moreover, when the temperature falls, saturation vapor pressure also decreases, which causes condensation within the reserve tank and piping. When the temperature becomes extremely low, the condensed water freezes, which can cause breakage or failure of the system. Another problem is that a large amount of energy remains in the compressed air discharged from the start control system during operation of the same, and noise produced by the discharge can become considerably large untoward noise. Still another problem is that it is required to carry out the engine start operation by the ignition key to restart the engine.
On the other hand, the conventional start control systems of the type which is applied to the hybrid vehicle are each required to be provided with a large-sized electric motor and a large-capacity battery which are very expensive and heavy, which results in considerable increases in the weight and manufacturing costs of the system.
It is an object of the invention to provide a start control system for an internal combustion engine, which is capable of automatically restarting the engine while ensuring excellent startability and fuel economy of the engine, and permits reduction of the size of the system, to reduce the weight and manufacturing costs of the system.
To attain the above object, the present invention provides a start control system for an internal combustion engine, comprising:
an electric motor;
an oil pump driven by the electric motor;
an accumulator for accumulating oil pressure delivered from the oil pump;
an oil passage through which the oil pressure is transmitted;
a hydraulic actuator connected to the accumulator via the oil passage and driven by the oil pressure accumulated in the accumulator, for starting the engine;
an oil pressure supply control valve arranged across the oil passage, for controlling supply of the oil pressure to the hydraulic actuator; and
control means for controlling operation of the oil pressure supply control valve to thereby cause the hydraulic actuator to start the engine.
According to this start control system for an internal combustion engine, the oil pump is driven by the electric motor, and oil pressure delivered from the oil pump is accumulated in the accumulator. When the engine is to be started, the control means controls the operation of the oil pressure supply control valve to cause the oil pressure to be supplied from the accumulator to the hydraulic actuator. As a result, the hydraulic actuator is driven to start the engine. In the start control system of the invention, the oil pressure generated by the electric motor is utilized to start the engine as described above, so that even during stoppage of the engine, it is possible to operate the electric motor to thereby accumulate oil pressure in the accumulator in preparation for the next start of the engine. Thus, differently from the conventional start control system using compressed air, the system of the invention can ensure excellent startability of the engine without suffering from a problem that the engine cannot be started properly when it is started next time after the stoppage.
Further, for the same reason, the system of the present invention is capable of generating higher pressure than the prior art using compressed air, so that the entire accumulator can be reduced in size, which permits the system to be designed to be more compact. Moreover, in general, a hydraulic actuator is capable of generating a larger driving force than an electric motor conventionally used for a starter of the engine, so that it is possible to increase the rotational speed of the engine during a cranking time to a desired rotational speed which is higher than that in the prior art, e.g. a rotational speed higher than an idling rotational speed. At the same time, the large driving force makes it possible to shorten a time period which the engine takes to reach the desired rotational speed, thereby reducing vibrations caused by the engine and noises produced by the driving system during the start of the engine. Further, since the start control system of the invention uses oil as a working medium, and the oil is smaller than the air in volume change caused by a pressure change, energy remaining in oil discharged from the system is smaller than energy conventionally remaining in the discharged compressed air, which makes it possible to reduce noises produced during the discharge of the working medium. For the same reason, the system of the invention is also capable of preventing freezing and breakage of the system due to the freezing, differently from the prior art using the air as a working medium. In addition, the system of the present invention is only required to be provided with an electric motor capable of generating torque for driving the oil pump for rotation and a battery capable of driving the electric motor, so that a large-sized electric motor and a large-capacity battery which are used in the conventional start control system applied to hybrid vehicles can be dispensed with. This makes it possible to reduce the size and weight of the system, which contributes to reduction of the manufacturing costs of the same. The above features and advantages ensure high marketability of the system.
Preferably, the start control system further comprises engine rotational speed-detecting means for detecting an engine rotational speed of the engine, and
the control means controls the operation of the oil pressure supply control valve such that the supply of the oil pressure to the hydraulic actuator is stopped when the detected engine rotational speed has exceeded a predetermined rotational speed after the supply of the oil pressure to the hydraulic actuator was started.
According to this preferred embodiment, the supply of oil pressure to the hydraulic actuator is stopped by the control means when the detected engine rotational speed has exceeded a predetermined rotational speed. Therefore, it is possible to start the engine reliably by properly setting the predetermined rotational speed to a desired rotational speed. Further, in the start control system using the hydraulic actuator, even after the engine rotational speed has exceeded the predetermined rotational speed, and it is instructed that the supply of oil pressure to the hydraulic motor be stopped, the hydraulic actuator continues to drive the engine, e.g., due to a time lag in operation of the oil pressure supply control valve, whereby the engine rotational speed is further increased. Therefore, it is possible to set the predetermined rotational speed to a value slightly lower than the desired rotational speed, allowing for the increase in the engine rotational speed. This makes it possible to shorten a time period for supplying the oil pressure to the accumulator, thereby preventing unnecessary reduction of the oil pressure accumulated in the accumulator. As a result, the time over which the electric motor is operated can be shortened, and consumption of electric power can be reduced.
More preferably, the start control system further comprises engine temperature-detecting means for detecting an engine temperature of the engine, and
the predetermined rotational speed is set to be higher as the detected engine temperature is lower.
In general, in an internal combustion engine, as the engine temperature is lower, the viscous resistance of lubricating oil becomes larger to increase viscous friction in the engine, and it becomes harder to effect ignition, so that when the engine temperature is low, the startability of the engine is lower than under normal starting conditions. Therefore, according to the above preferred embodiment, the predetermined rotational speed is set to be higher as the detected engine temperature is lower, whereby the engine can be properly started dependent on the engine temperature at the time of start of the engine.
Also more preferably, the start control system further comprises a stop time period-determining means for determining whether or not a stop time period over which the engine has been in stoppage before a start of the engine is longer than a predetermined time period, and
when the stop time period-determining means determines that the stop time period is longer than the predetermined time period, the predetermined rotational speed is set to a first predetermined rotational speed, whereas when the stop time period-determining means determines that the stop time period is equal to or shorter than the predetermined time period, the predetermined rotational speed is set to a second predetermined rotational speed which is lower than the first predetermined rotational speed.
In general, when a stop time period of the engine is short, a decrease in the engine temperature is small, and hence, the viscous friction in the engine is also small. Further, a decrease in the oil temperature within the system is also small, and hence the responsivity of the hydraulic actuator is high. In view of this, according to the above preferred embodiment, when the stop time period is shorter than the predetermined time period, the engine rotational speed at the stoppage of the supply of oil pressure to the hydraulic actuator is set to the second predetermined rotational speed which is lower than the first predetermined rotational speed. As a result, excellent startability of the engine can be maintained according to the stop time period before the start of the engine, and at the same time, since the time period for supplying oil pressure to the hydraulic actuator can be shortened, it is possible to utilize oil pressure within the accumulator efficiently.
Preferably, the start control system further comprises misfire-detecting means for detecting a misfire of the engine, and
the control means controls the operation of the oil pressure supply control valve such that the supply of the oil pressure to the hydraulic actuator is stopped, depending on an output from the misfire-detecting means.
Preferably, the control means controls the operation of the oil pressure supply control valve such that the supply of the oil pressure to the hydraulic actuator is stopped when a first predetermined time period has elapsed after the supply of the oil pressure to the hydraulic actuator was started.
According to this preferred embodiment, oil pressure is continuously supplied to the hydraulic actuator until the predetermined time period has elapsed after the start of the supply of oil pressure. Therefore, it is possible to start or crank the engine reliably by setting the predetermined time period to a time period allowing the engine rotational speed to be positively increased to the desired rotational speed at which the engine performs its self-sustaining operation. Further, because the supply of oil pressure to the hydraulic actuator is stopped when the first predetermined time period has elapsed, even if the engine rotational speed does not reach the desired rotational speed due to a failure or breakdown of the engine, it is possible to utilize the oil pressure within the accumulator efficiently without wasting the same.
The start control system further comprises engine temperature-detecting means for detecting an engine temperature of the engine, and the first predetermined time period is set to be longer as the detected engine temperature is lower.
In general, when the engine temperature of the engine is low, viscous friction is large, and hence, the responsivity of the hydraulic actuator is low, which makes it difficult to start the engine. Therefore, according to the above preferred embodiment, the time period over which the hydraulic actuator is driven is set to be longer as the engine temperature is lower, whereby the engine can be started properly according to the temperature.
Preferably, the start control system further comprises:
a starter switch,
manual operation-determining means for determining whether or not a driver has operated the starter switch after stoppage of the engine,
start intention-determining means for determining whether or not the driver has an intention to start a vehicle on which the engine is installed, based on operating conditions of the engine after the stoppage of the engine, and
engine rotational speed-detecting means for detecting an engine rotational speed of the engine, and
when the manual operation-determining means determines that the starter switch has been operated, the control means controls the operation of the oil pressure supply control valve such that the supply of the oil pressure to the hydraulic actuator is stopped when the detected engine rotational speed has exceeded a third predetermined rotational speed after the supply of the oil pressure to the hydraulic actuator was started, while when the start intention-determining means determines that the driver has the intention to start the vehicle, the control means controls the operation of the oil pressure supply control valve such that the supply of the oil pressure to the hydraulic actuator is stopped when the detected engine rotational speed has exceeded a fourth predetermined rotational speed lower than the third predetermined rotational speed after the supply of the oil pressure to the hydraulic actuator was started.
According to this preferred embodiment, it is possible not only to manually start the engine after the stoppage of the same, by operation of a starter switch by the driver, but also to automatically start the engine based on the operating conditions of the same, in response to the driver""s intention to start the vehicle. In an internal combustion engine of this type which can be automatically restarted after a stoppage, a stop time period before the restart of the engine is generally shorter than a stop time period before the manual start of the engine, and hence, the engine temperature is higher, making the engine easier to start. Therefore, by setting the predetermined rotational speed as a desired rotational speed for the automatic restart to be lower than that for the manual start, it is possible to ensure excellent startability of the engine for both the automatic restart and the manual start. Moreover, by setting the predetermined rotational speed to a low speed at the restart, it is possible to further shorten the time period for supplying oil pressure to the hydraulic actuator.
More, preferably, the start control system further comprises a stop time period-determining means for determining whether or not a stop time period over which the engine has been in stoppage before a start of the engine is longer than a predetermined time period, and
the fourth predetermined rotational speed is set depending on determination of the stop time-determining means.
Preferably, the start control system further comprises:
a starter switch,
manual operation-determining means for determining whether or not a driver has operated the starter switch after stoppage of the engine, and
start intention-determining means for determining whether or not the driver has an intention to start a vehicle on which the engine is installed, based on operating conditions of the engine after the stoppage of the engine, and
when the manual operation-determining means determines that the starter switch has been operated, the control means controls the operation of the oil pressure supply control valve such that the supply of the oil pressure to the hydraulic actuator is stopped when a second predetermined time period has elapsed after the supply of the oil pressure to the hydraulic actuator was started, while when the start intention-determining means determines that the driver has the intention to start the vehicle, the control means controls the operation of the oil pressure supply control valve such that the supply of the oil pressure to the hydraulic actuator is stopped when a third predetermined time period which is shorter than the second predetermined time period has elapsed after the supply of the oil pressure to the hydraulic actuator was started.
As described hereinbefore, in an internal combustion engine of the type which can be automatically restarted after a stoppage, the engine is generally easier to start at the time of restart than at the time of manual start, and hence a time period required for the restart of the engine is shorter. Therefore, according to this preferred embodiment, the time period over which the hydraulic actuator is driven for the restart of the engine is set to be shorter than that for the manual start, whereby excellent startability of the engine can be ensured for both the restart and the manual start. Further, the embodiment makes it possible to shorten the time period for supplying oil pressure to the hydraulic actuator, thereby reducing electric power consumed by the electric motor.
More preferably, the start control system further comprises oil pressure-determining means for determining whether or not the oil pressure accumulated in the accumulator is sufficient for starting the engine, and pressure control means for controlling the electric motor such that the electric motor drives the oil pump until the oil pressure accumulated in the accumulator becomes sufficient for starting the engine, when the oil pressure-determining means determines that the oil pressure accumulated in the accumulator is not sufficient for starting the engine.
The above and other objects, features, and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.